1. Field of the Invention
The present invention relates to indicating devices and, more particularly, is directed towards humidity indicators.
2. Description of the Prior Art
Humidity indicators of various configurations have been introduced with varying degrees of success. A humidity indicator utilizing a polyamide resin sensing element which cooperates with a flexible diaphragm in displacing a tranduction fluid constrained within a capillary tube is disclosed in a final report entitled "Development Of A Low-Cost Humidity Indicator For Packaging." The humidity indicator configuration described therein requires that a barrier liquid and a transduction liquid be filled sequentially through a single orifice which could result in entrained bubbles. A sliding seal, which is prone to leakage under pressure, is provided for a calibration screw which projects into and acts directly on a reservoir containing the transduction fluid. An adhesive bond that is provided between the sensing element and diaphragm tends to separate partially and degrades instrument accuracy. In high humidity environments, i.e. greater than 70% relative humidity, the barrier liquid overflows into the housing and does not retract uniformly within the capillary tube when the humidity decreases. In consequence, bubbles and voids formed in the barrier liquid enter the transduction fluid and cause a breakup of the capillary column. A need has arisen for improvements in humidity indicating devices.